Basics:
-Two rows of leads from different time zones. (One row if they're really active).
-Don't pass leadership no matter what.
-Have ally guilds as sub guilds.
-Main a tower (consistency is important).
-Don't spam guild chat, important messages may be swamped by useless messages.
-Optional: Alliances/truces with other strong guilds that dominate.

Note: There are no guild rewards currently so really there won't be a lot of good people joining right now (since most people want to play for rewards), once the new guild rewards system is implemented then there will be an influx of competing guilds again.